1. Field of the Invention
The present invention relates to a touch panel and more particularly to a scan method for increasing frame rate of touch panel and touch panel device using the same.
2. Description of the Related Art
With reference to FIG. 8A, a touch panel 60 has multiple driving lines Tx1˜Tx4 and multiple sensing lines Rx1˜Rx4. The driving lines Tx1˜Tx4 are connected to a driving circuit 70. The sensing lines Rx1˜Rx4 are connected to a sensing circuit 80.
With reference to FIG. 5B, the driving circuit 70 drives the driving lines Tx1˜Tx4 within a scan time. The scan time TSCAN has multiple detection cycles TD, and an excitation signal is outputted to a driving line within each detection cycle TD. When each driving line Tx1˜Tx4 receives an excitation signal outputted from the driving circuit 70, the sensing circuit 80 connected to the sensing lines Rx1˜Rx4 starts receiving sensing signals. With reference to FIG. 8C, each sensing line Rx1˜Rx4 generates a voltage or current variation upon a rising edge t and a falling edge t2 of each cycle of any excitation signal. Hence, given the sensing line Rx2 as an example, the receiving circuit 80 can perform signal sampling at the rising edge t1 or the falling edge t2 to acquire a sensed capacitance value −C22 on the sensing line Rx2.
From the foregoing description, if no touch object is available on the touch panel 60, the capacitance value −C22 can be sensed at sensing points intersected by the driving lines Tx1˜Tx4 and the sensing lines Rx1˜Rx4 as a result of the excitation signal. With reference to FIG. 9, suppose that a touch object appears on a sensing point intersected by the driving line Tx2 and the sensing line Rx2. As the touch object is a good conductor of electricity, it will absorb a part of energy stored at the sensing point indicated by Tx2 and Rx2 arising from the excitation signal. Hence, the capacitance value sensed by the sensing circuit 80 is −C22+ΔC22, which is a capacitance variation normally used to identify if a touch object is present.
With reference to FIG. 10, to enhance the signal-to-noise ratio (SNR), the driving circuit sequentially outputs K excitation signals within each detection cycle TD with each excitation signal having an excitation cycle TE, so that TD K*TE. Hence, after the completion of each detection cycle TD, each sensing circuit can sample K capacitance values, and the K capacitance values are summed up to enhance the SNR.
However, such detection method is disadvantageous to a frame rate of large-scale touch panel. Given TE≧10RC as an example, each driving line needs to take an amount of time K×10RC to finish scan, and the driving circuit sequentially outputs K excitation signals to the driving lines with only one of the driving lines being driven within the detection cycle. As a large-scale touch panel has more driving lines than a relatively smaller touch panel, if the large-scale touch panel has N driving lines, finishing the scan of all driving lines should take at least an amount of time N×K×10RC. Accordingly, the frame rate of the large-scale touch panel is inevitably extended and a delay in operation is caused.